The present invention generally relates to apparatus for controlling heating and ventilating equipment, and more particularly for controlling heating and ventilating units and associated equipment that are often used in individual rooms of schools and the like, often referred to in the art as unit ventilators.
In the art of heating, ventilating and air conditioning (HVAC) for buildings and the like there has been a continuing effort in developing more accurate and sophisticated controls for accurately controlling the systems to provide more accurate control in terms of maintaining the desired temperature within a space, and minimizing the energy required to provide heating and/or air conditioning, and in providing increased safety. With the increased utilization of computers, such systems can now be controlled by what had been considered to be complex control schemes that had been used in only very expensive, sophisticated supervisory and control systems. In many of such systems, pneumatic pressure control lines extended between components of the system for controlling the operation of the system. The use of such pneumatic lines has existed for decades and systems using the same continue to be installed. As a result of the long use of such pneumatic control lines, there are thousands of systems in existence which are desirable targets for upgrading in the sense that more sophisticated control may be desirable from a cost benefit analysis, given the relatively inexpensive and robust technical capabilities of control systems compared to the seemingly ever increasing cost of energy for providing heating and air conditioning.
Apart from these general considerations, there are many buildings that exist which often are heated in the winter, but because they have little usage in the summer months and other reasons, true air conditioning is not provided in them. A prime example is that of school buildings which have many classrooms that are heated by individual heating units, which are commonly known as unit ventilators. Such unit ventilators are generally connected to a heating plant that communicates heat to the ventilators via a heated fluid, such as hot water or steam lines, although electrical heating elements are sometimes employed.
With the unit ventilators being located in each room, many older unit ventilators are not conducive to being controlled by a single supervisory and control system, except to the extent that the pneumatic control lines can be switched between nominal pressure values which reflect differing set points for day or night operation and the pneumatic lines can be controlled from a common pressure source. Pressure detectors in the unit ventilators are adapted to sense the difference between the day/night nominal pressures and therefore provide some degree of control, albeit not overly sophisticated. The temperature control of the rooms is provided by a pneumatic thermostat located within the room at some distance from the unit ventilator so that it provides a fair reading of the temperature of the room rather than the discharge temperature of the air that flows from the unit ventilator.
Unit ventilators generally have a damper for controlling the admission of air from outside the room, and also typically employ a fan which forces air through the ventilator which obviously includes heating coils.
Such unit ventilators have generally not employed sophisticated control schemes, and the control has largely consisted of using the room thermostat for modulating the flow of heat through the heating coils of the unit ventilator. This is particularly true with respect to unit ventilators that have been installed for some time.
Accordingly, it is a primary object of the present invention to provide an improved controller for use with unit ventilators of the type described above, which employs sophisticated and effective cascaded control.
A related object is to provide such an improved controller which incorporates a processing means and is adapted to utilize a relatively complex and sophisticated cascaded control scheme in the operation of the controller.
Another object of the present invention is to provide a unit ventilator that has cascaded control, and utilizes input parameters that include signals that are generated that are indicative of the pneumatic output line control pressure, the room temperature, the temperature of the air immediately downstream of the heating coils, i.e., the discharge temperature of the unit.
A more specific object of the present invention is to provide such an improved controller that utilizes the sensed room temperature and a room temperature set point to generate a set point for the temperature of the air being discharged from the unit ventilator, and utilizing the discharge temperature set point and the sensed discharge temperature to control the damper position and the operation of the heating coils of the unit ventilator.
Still another object of the present invention is to provide such an improved unit ventilator controller which employs a proportional gain factor, an integral gain factor and a derivative gain factor (a PID control loop) in its operation.
Yet another object of the present invention is to provide such an improved unit ventilator controller which employs two cascaded PID control loops in the control of the unit ventilator itself.
Another object of the present invention is to provide such an improved unit ventilator controller which employs cascaded PID control loops in the control of auxiliary radiation means, if such is employed.
Still another object of the present invention is to provide an alternative embodiment of an improved unit ventilator controller that utilizes cascaded PID control loops in an ASHRAE cycle 3 type of operation wherein independent control of the position of the damper and of operation of the heating coils of the unit ventilator.